Molecular and crystal structure of cis-bis(L-hydroxyprolinato)-copper(II) tetrahydrate and trans-bis(D-allohydroxyprolinato)-copper(II)–water(2/5)

Abstract

The structures of cis-bis(L-hydroxyprolinato) copper(II) tetrahydrate (1) and trans-bis(D-allohydroxyprolinato) copper(II)–water(2/5)(2) have been determined by X-ray analysis. These compounds provide an unusual example of epimeric amino acids supporting different geometrical arrangements in the copper(II) square plane. Crystals of complex (1) are monoclinic, space group P2₁, a= 10.209(6), b= 8.071(3), c= 9.698(3)Å, β= 100.33(4)°, and Z= 2. Crystals of complex (2) are orthorhombic, space group P2₁2₁2₁, a= 8.678(5), b= 17.737(4), c= 18.686(7)Å, and Z= 8, with two molecules per asymmetric unit. Both structures were solved by Patterson and difference electron-density syntheses. Final R values of 0.037 for 2 248 reflections and 0.045 for 2 207 reflections were obtained for complexes (1) and (2) respectively. In both structures each copper atom has an essentially square-planar environment with the hydroxyproline co-ordinating by the pyrrolidine nitrogen and carboxylate oxygen. A distorted six-fold co-ordination is completed by weak Cu ⋯ O interactions. The Cu–N, Cu–O bond lengths and Cu ⋯ O axial distances in the two structures are within the range observed in similar complexes. Extensive systems of hydrogen bonding are present in both structures.